The present invention relates especially to hydrodynamic bearings, and more specifically to methods and apparatus for the assembly of such bearings which takes into account the close tolerances of such bearings.
The use of hydrodynamic bearings in many contexts such as spindle motors for disc drives has become increasingly popular. In a hydrodynamic bearing, a lubricating fluid such as air, gas or oil provides a bearing surface between two relatively rotating members, typically a shaft and surrounding sleeve. Hydrodynamic bearings are characterized by establishing a bearing interface over a large surface area in comparison to a ball bearing assembly which comprises a series of point interfaces. This is desirable because the increased bearing surface reduced wobble or runout between the rotating and fixed members. However, this increased bearing surface also leads to a problem, in that the gap between the fixed and rotating surface can be very small, in the order of 2-7 xcexcm size gaps. Thus, the tolerances in a hydrodynamic bearing are roughly five times smaller than in a ball bearing. A fixture which can accurately and repeatably set these gaps while allowing for high speed assembly is highly desirable.
Therefore, it is an object of the present invention to provide an improved apparatus for and method of assembly of a hydrodynamic bearing.
It is a related objective of the invention to create an improved method for accurately setting the gap between the shaft and sleeve which define a hydrodynamic bearing.
A further and related object of the present invention is to provide a method and apparatus for setting the bearing gap in a hydrodynamic bearing without the need for as many small tolerances on individual bearing components as normally associated with such an assembly.
These and other objectives and advantages of the present invention are achieved by utilizing an air gage to measure the pressure drop (and indirectly the flow rate) of air through the bearing; while facing sections of the air bearing are moved closer together. The measured pressure drop can be correlated to the actual bearing gap and monitored to determine when the proper gap has been achieved.
More particularly, the inner and outer elements of the bearing are clamped in separate carriers and are held in place. The carriers are then moved toward one another so that the inner or shaft portion of the bearing slides into the outer or sleeve portion of the bearing. To accurately set the gap between the two, an air hose with an air gage attached to it is attached to one end of the bearing gap; air is pumped through the bearing gap, exiting through the opposite end of the gap. Preferably, an air gage is attached which is of the type which can be calibrated to register 0 when the air flow into one end of the gap equals the air flow out the other end of the gap. By testing a set of reference motor parts, a high end and a low end of an acceptable bearing gap range can be established, and the corresponding air gage readings obtained. Thus, once the air gage has been calibrated against a minimum and maximum gap, each motor can be assembled with the proper gap by simply adjusting the relative position of the parts until a target air gage reading or a reading between the high and low end of an acceptable range is obtained.
Other features and advantages of the present invention would become apparent to a person of skill in the art who studies the present invention disclosure. Therefore, a more detailed description of a preferred embodiment of the invention is given with respect to the following drawings.